Fix P2122: Mechanic’s solutions that WORKED

The code P2122: Throttle/Pedal Position Sensor/Switch “D” Circuit Low Input points out a fault in the circuit connected to the Accelerator Pedal Position Sensor, indicating that the input signal received is lower than expected. This fault is most likely caused by an issue with the sensor itself, its wiring, or the Powertrain Control Module (PCM) interpreting its signal.

P2122 quick overview

Meaning	P2122: Throttle/Pedal Position Sensor/Switch “D” Circuit Low Input
Is it serious?	This code can be serious as it relates to the vehicle’s acceleration and response, potentially leading to dangerous driving conditions if not addressed promptly.
Possible causes	– Faulty Accelerator Pedal Position Sensor – Damaged or corroded wiring and connectors – Faults within the PCM or its software – Ground connection issues
How to diagnose?	Inspect APPS/TPS: Check the Accelerator Pedal Position Sensor/Throttle Position Sensor for any signs of damage or wear. Check Wiring and Connectors: Thoroughly inspect all related wiring for shorts, frays, or disconnections. Consult TSBs: Look for any Technical Service Bulletins related to this issue for your specific vehicle model. Perform Relearn Procedure: After any repair or replacement, conduct necessary relearn procedures for the system. Reprogram/Reflash PCM: Ensure the PCM is up-to-date with the latest software. Verify Sensor Supply Voltage: Check the 5V reference and other power supplies to the sensor. Check for Rodent Damage: Inspect the vehicle for any signs of rodent damage, particularly around the wiring harness.

How to fix P2122 – learn from mechanics

I looked into P2122 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: GMC

Vehicle Information:
2014 GMC Terrain SLE 2.4L

Issue + Repair History:

• The vehicle was experiencing hesitation due to a bad sensor.
• The accelerator pedal needed replacement, but access was difficult due to the heater box and the bracket’s design.

Related Repair History:

• None prior to this issue.

Other OBD2 Codes + Test Results:

• P2122: APP Sensor

Suggestions to Fix Issue:

• Follow the factory procedure for removing the instrument panel insulator and the Communication Interface Module to access the accelerator pedal.
• Use a 1/4 drive flex socket and swivel setup to reach the bolts.
• Consider charging more for the labor-intensive job due to its difficulty.
• If unable to access easily, have a younger or more agile technician with the right tools take on the task.

Final Fix:

• The accelerator pedal was successfully replaced after about an hour and a half of work using 1/4 inch drive tools and a ratchet wrench.
• Acknowledged the design was challenging and noted the importance of having the right tools and technician for such tasks.

Case #2: Dodge

Vehicle Information:
2004 Dodge Ram 3500 ST 5.9L

Issue + Repair History:

• The truck experienced low power and set code P2122 (APP circuit low).
• The issue intensified under load, with APP% readings fluctuating significantly when ascending hills.
• About 6 months prior, a new in-tank pump was installed.

Other OBD2 Codes + Test Results:

• P2122: APP circuit low
• Sensor ground: 0 volts (good)
• TP signal: 0.49 – 4.3V smooth
• TP sensor return: 0V (good)
• 5-volt supply: 5V
• Idle switch: 4.995V constantly

Suggestions to Fix Issue:

• Replace the Accelerator Pedal Position Sensor (APPS), as it’s often the solution for this code and symptom.
• Double-check the fuel tank pickup, especially since it was serviced recently, to ensure it wasn’t damaged during installation.

Final Fix:

• Replacing the APPS resolved the issue.
• After replacement, testing under similar conditions showed a consistent 100% reading and increased power.

Case #3: Ford

Vehicle Information:
2015 Ford Focus ST 2.0L

Issue + Repair History:

• The vehicle exhibited hesitation and surging, setting code P2122 frequently but intermittently.
• This issue most commonly occurred under load and at startup.
• Initially, a short in the APP VREF 1 signal was observed, lasting approximately 10ms during cranking and shutting off.
• Replaced and reflashed the PCM, but the problem persisted.

Other OBD2 Codes + Test Results:

• P2122: Throttle/Pedal Position Sensor/Switch D Circuit Low Input
• P6A6: Sensor Reference Voltage A Circuit Range/Performance
• Testing showed APP VREF 1 shorting to ground during crank.

Suggestions to Fix Issue:

• Check live data for throttle body and accelerator pedal position sensors.
• Consider potential issues with the throttle body, including carbon buildup.
• Ensure all 5V sensors are functioning correctly and not contributing to the short.
• Compare with another vehicle to verify if the short is a normal operation by the PCM.
• Consider the throttle assembly for defects, particularly internal gears.
• Reexamine the testing procedure for grounds, ensuring they are tested under load.

Final Fix:

• Cleaning all grounds associated with the PCM, chassis, and engine resolved the issue.
• After thorough cleaning, the problem went away, indicating that the initial ground testing may not have been sufficient or performed under the correct conditions.

Case #4: Nissan

Vehicle Information:
2003 Nissan 350Z Track 3.5L

Issue + Repair History:

• The car experienced poor idle quality, hesitation, stalling, and the MIL lamp was on.
• Numerous codes were set, including P2122, P2138, P0223, P0123, P2135, and P0507.
• The throttle body was replaced twice, and the accelerator pedal position sensor was replaced and reprogrammed.
• The issue persisted after these repairs, leading to further investigation.

Other OBD2 Codes + Test Results:

• P2122: APP sensor
• P2138: APP sensor 1/circuit
• P1229: Sensor power/circuit
• P2135: TP sensor
• P0223: TP sensor 1/circuit
• P0123: TP sensor 2/circuit
• TP ref white/red: 5.02 volts consistently

Suggestions to Fix Issue:

• Check the alternator for overcharging issues which can cause system codes and failsafe.
• Investigate other items on the same power circuit as APP sensor #1 for potential shorts affecting the system.
• Inspect the wiring harness for damage, particularly near the refrigerant pressure sensor.
• Perform an idle air relearn procedure after replacing the throttle body.
• Consider potential rodent damage to the engine room wiring harness.

Final Fix:

• The car was fixed by locating and addressing a wiring issue near the refrigerant pressure sensor.
• Cleaning and ensuring all connections and grounds associated with the affected circuits resolved the erratic behavior and code P1229.

Case #5: Ford

Vehicle Information:
2004 Ford Explorer NBX 4.0L

Issue + Repair History:

• The vehicle displayed codes P2121, P2122, and P2123, and ran sluggishly.
• Previously, another technician replaced the accelerator pedal assembly and the PCM, both sourced from Ford.
• The vehicle was sent to Ford for PCM reprogramming.

Related Repair History:

• Replaced PCM and accelerator pedal assembly with Ford parts.

Other OBD2 Codes + Test Results:

• P2121: Accelerator Pedal Performance
• P2122: Accelerator Pedal Performance sensor 1 voltage low
• P2123: Accelerator Pedal Performance sensor 1 voltage high

Suggestions to Fix Issue:

• Inspect wiring for damage, especially for rodent damage or nests near the firewall.
• Perform a pinpoint test to check for resistance, shorts, or open circuits in the harness.
• Ensure the throttle assembly is properly reprogrammed and goes through a relearn procedure.

Final Fix:

• Sending the vehicle to the dealer for PCM reprogramming and undergoing a relearn procedure resolved the issue.
• After these measures, the vehicle drove fine and the codes did not return.

Common Advice	Brief Description of Diagnostic Step
Replace APPS/TPS	If diagnostics confirm, replace the Accelerator Pedal Position Sensor or Throttle Position Sensor.
Inspect Wiring and Connections	Thoroughly check wiring for shorts, opens, or damage, especially between the sensor and the PCM.
Check for Rodent Damage	Inspect the vehicle for signs of rodent infestation or damage, particularly near wiring harnesses.
PCM Reprogram/Reflash	Ensure the PCM is up-to-date with the latest software and reprogram or reflash if necessary.
Perform Relearn Procedure	After parts replacement or reprogramming, perform necessary relearn procedures for the throttle body or pedal position.
Consult Technical Service Bulletins (TSBs)	Look up any relevant TSBs that might address known issues with the vehicle model related to the P2122 code.
Check for Ground Issues	Ensure all grounds are clean and secure, as poor grounding can lead to erratic sensor readings and set codes.
Verify Sensor Supply Voltage	Check the 5V reference and other supply voltages to the sensors to ensure they are within specifications.